1. Field of the Invention
The present subject matter relates generally to a wavelength selective switch (WSS) apparatus including a multi-layer reflector, and more specifically, to a WSS apparatus including a multi-layer reflector having a plurality of layers formed with a plurality of pixels that are controllable by a reflection controller.
2. Description of the Related Art
In optical communications systems, the use of wavelength selective witching for applications of optical cross-connects has attracted much interest because of the goal of fully flexible, networks where the paths of each wavelength can be reconfigured to allow arbitrary connection between nodes with the capacity appropriate for that link at a particular point in time.
Conventional optical switches are typically based on optical-electrical-optical (OEO) conversion technologies. In an OEO scheme, the optical signal is transduced into an electrical signal, the signal is switched electrically, and is reconverted back into a new optical beam. Unfortunately, the OEO conversion is limited by the processing speed of the available electronics. Furthermore, OEO devices are dependent on wavelength, modulation format, and modulation frequency.
More recently, there has been increased interest in all-optical switching, in which one or more wavelengths are selectively switched without the need to convert the optical signals to an electronic signal. Micro-electro-mechanical systems (MEMS) have played an important part in all-optical switching since these miniature actuators can be designed to simultaneously switch spatially resolved portions of the optical signal independently from each other. Furthermore, MEMS devices can be designed to be compact, have a low power consumption, and can be mass produced to produce a low cost switch. Liquid crystal (LC) modulators have played an important role in all-optical switching for similar reasons.
In many prior art switches using MEMS or LC modulators, the switch includes a dispersive element to spatially separate the multiplexed beam of light into individual communication channels, which are independently modified by the modulator. The dispersive element is typically a reflective or transmissive diffraction grating used in either a single pass or double pass configuration. For example, in the single pass configuration a first diffraction grating performs the demultiplexing while a second diffraction grating performs the multiplexing. In the double pass configuration, a single diffraction grating is combined with a reflector to provide demultiplexing in a first pass therethrough and multiplexing in the second pass therethrough.
U.S. Pat. No. 7,014,326 to Danagher et al. for “Wavelength Blocker” describes the basic principles of a wavelength blocker, which is capable of blocking a variable number of non-consecutive channels. U.S. Pat. No. 7,720,329 to Presley et al. for “Segmented Prism Element and Associated Methods for Manifold Fiberoptic Switches” describes a fiber optic switch utilizing a segmented prism element, including a fiber optic switch used in multi-channel optical communications networks and having one or more arrays of micro electromechanical system (MEMS) mirrors. U.S. Pat. No. 8,401,348 to Boduch for “Methods and Apparatus for Constructing Large Wavelength Selective Switches Using Parallelism” describes constitution of a large wavelength selective switch (WSS) system by coupling small port WSSs. U.S. Pat. No. 7,492,986 to Kelly for “Apparatus and Method for Optical Switching with Liquid Crystals and Birefringent Wedges” describes the switching of optical signals using liquid crystals (LCs) and a birefringent wedge.
U.S. patent application Ser. No. 14/055,171, filed by the applicant on Oct. 16, 2013, published by U.S.P.T.O. on Apr. 17, 2014, is directed to a WSS including an LCOS for selectively diverting a certain wavelength component of light beams to continue to propagate and keeping another wavelength component of the light beams from propagating by controlling a voltage applied thereto and/or a polarization of the light beams. In accordance with such WSS structure, accurate control of the output angle of the beams can be realized. In addition, since it utilizes a polarization mode in the attenuation domain, any crosstalk between the domains, which happened when adopting conventional phase mode attenuation, can be prevented.